1. Field of the Invention
The present invention relates to a magnetic recording medium for use in a large-capacity memory, an electronic filing-system or the like, and a method for producing the same.
2. Related Background Art
The magnetooptical recording medium is already known as an erasable recording medium. Crystalline materials such as garnet and intermetal compounds such as MnBi were investigated as the material for forming such magnetooptical recording media but recent developments are directed toward a recording layer utilizing rare earth elements such as Tb, Gd and Dy and alloys of transition metals such as Fe and Co. The rare earth-transition metal alloy film has various advantages such as a large magnetooptical effect, a freedom in the selection of Curie temperature (substantially equal to recording temperature) by the adjustment of the composition, and absence of noise resulting from the grain boundary inherent to crystalline materials.
On the other hand, the deterioration of recording characteristics in prolonged storage or use is a major concern because the rare earth elements are very active and apt to undergo deteriorating reactions such as oxidation or nitrogeneration even at room temperature.
The current countermeasure consists of the addition, to the materials constituting the recording layer, of an additive capable of improving the anticorrosive resistance such as Ti, Cr or Al, but it is impossible to obtain sufficient anticorrosive power without sacrificing the magnetooptical effect and the vertical magnetic anisotropy. Therefore, as a second best measure, there is employed a method of sandwiching the recording layer with the elaborate protecting film such as oxide, nitride or carbide films.
However, since the recording layer itself is easily deteriorated by reaction, it is significantly influenced, in the process of formation of the recording layer, by the gas emitted from the substrate, or the gas remaining in the vacuum chamber, and the variation of magnetic properties is inevitable with several days to several months after the preparation of the magnetooptical recording medium.